EP 1 234 110 B1 describes a pressure determination device by means of which the pressure in the fuel storage arrangement can be determined and a potential leak in the fuel storage arrangement can be detected. The pressure determination device, in this case, is connected by means of a connection element to the activated charcoal canister of the fuel storage arrangement. The activated charcoal canister is connected to a fuel tank of the fuel storage arrangement by means of a line through which gaseous fuel can flow. The activated charcoal filter is designed for storage of gaseous hydrocarbons. To regenerate the activated charcoal canister, a shutoff valve is opened in a supply line to the activated charcoal canister and at the same time a regeneration valve is opened in a discharge line which leads away from the activated charcoal canister. A negative pressure in the discharge line provides for discharge of the stored hydrocarbons from the activated charcoal canister.
To determine the pressure in the fuel storage arrangement for purposes of finding a leak in the fuel storage arrangement, the connection element is connected to the activated charcoal canister and the fuel storage arrangement is blocked fluid-tight. With declining temperature in the fuel storage arrangement, a negative pressure is established in the interior of the connection element. The negative pressure is transferred to the first chamber by way of a connecting line for communicating connection of the interior to the first chamber of the pressure determination device.
The pressure determination device has a second chamber in which atmospheric pressure prevails. The second chamber which is connected to the atmospheric air pressure of the exterior by way of another connection element is made separated fluid-tight from the first chamber and from the interior of the connection element. A membrane which separates the first chamber from the second chamber fluid-tight moves under the influence of the negative pressure in the first chamber, the membrane arching in the direction to the first chamber. Moving the membrane actuates a switch and a switching signal is produced. A time interval from connection of the connection element to the fluid-tight, blocked activated charcoal canister, until actuation of the switch and the initial temperature of the fuel storage arrangement are determined. Depending on the time interval and the initial temperature, it can be ascertained whether the negative pressure, which is being established in the fuel storage arrangement as a result of the decrease of the temperature, allows sufficient tightness of the fuel storage arrangement to be deduced.
In the operation of pressure determination devices of the type described, for example, in EP 1 234 110 B1, relatively rapid mechanical wear of the switch was observed.
The object of this invention is therefore to devise a pressure determination device and a method for operating a pressure determination device of the initially mentioned type in which there is especially good protection of the switch against damage.